As catalysts used for ammoxidation of organic compounds, various catalysts have hitherto been disclosed.
As catalysts for synthesis of acrylonitrile by ammoxidation of propylene, for example, Japanese Patent Application, Second Publication No. Sho 38-17967, discloses an oxide catalyst containing molybdenum, bismuth, and iron, while Japanese Patent Application, Second Publication No. Sho 38-19111, discloses an oxide catalyst containing iron and antimony.
These catalysts have been continuously and intensively improved and various catalysts containing rare earth elements as an essential component have been proposed.
For example, Japanese Patent Application, First Publication No. Sho 51-40391, Japanese Patent Application, First Publication No. Sho 59-204163, Japanese Patent Application, First Publication No. Hei 7-47272, Japanese Patent Application, First Publication No. Hei 7-51570, Japanese Patent Application, First Publication No. Hei 11-169715, Japanese Patent Application, First Publication No. 2000-5603 and Japanese Patent Application, First Publication No. 2001-114740 disclose catalysts containing molybdenum, bismuth, iron, and rare earth elements such as lanthanum, cerium, praseodymium and neodymium.
The Methods for preparing these catalysts have been studied so as to further improve the yield of the objective product.
For example, Japanese Patent Application, First Publication No. Hei 6-9530, discloses a method of heating a slurry containing molybdenum, bismuth, nickel, and cobalt at 90° C. for 3 hours, Japanese Patent No. 2520282 discloses a method of adjusting the pH of a slurry containing catalyst components to 5 or less, and Japanese Patent No. 2640356 discloses a method of adjusting the pH of a slurry containing molybdenum and iron to 5 or less and heat-treating the slurry at a temperature within a range from 50 to 120° C.
According to these methods for preparing a catalyst, some effect is exerted in respect of an improvement in yield of the target product and maintenance of reaction results for a long time; however, the effect is not industrially satisfactory. Therefore, it has been strongly desired to develop a catalyst which achieves high yield of the target product and can maintain high yield for a long time.
The present invention has been made to solve the problems described above, and an object of the present invention is to provide a method for preparing a catalyst which is useful for synthesis of nitrites by ammoxidation of organic compounds, especially synthesis of acrylonitrile by ammoxidation of propylene.